The luminous intensity of dark variant separated form photobacterium phosphoreum is 1/10000 less than that of wild-type. Ethidium Bromide (EB), Mytomycin C(MC), 2-amino fluorine can all strongly induce reversion mutation for S1 within 24h and increase reversion ratio significantly. The results of experiments indicated that these revertants have stable genetic character and the mutation may take place at gene levels. The mutagenesis to S1 caused by EB, MC and 2-AF was detected and it may be a new rapid, simple and sensitive method of gene toxicant monitoring.